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subroutine fpback(a,z,n,k,c,nest)
c subroutine fpback calculates the solution of the system of
c equations a*c = z with a a n x n upper triangular matrix
c of bandwidth k.
c ..
c ..scalar arguments..
integer n,k,nest
c ..array arguments..
real*8 a(nest,k),z(n),c(n)
c ..local scalars..
real*8 store
integer i,i1,j,k1,l,m
c ..
k1 = k-1
c(n) = z(n)/a(n,1)
i = n-1
if(i.eq.0) go to 30
do 20 j=2,n
store = z(i)
i1 = k1
if(j.le.k1) i1 = j-1
m = i
do 10 l=1,i1
m = m+1
store = store-c(m)*a(i,l+1)
10 continue
c(i) = store/a(i,1)
i = i-1
20 continue
30 return
end
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